Pain Management and CYP2D6/CYP2C19

Test code(s) 18946

Question 1. What is cytochrome P450 2D6/2C19?

Cytochrome P450 (CYP) is a family of enzymes that are involved in metabolism – including drug metabolism. Two of the more common enzymes are cytochrome P450 2D6 (CYP2D6) and cytochrome P450 2C19 (CYP2C19). Variations in the genes that code for these enzymes affect the rate and extent of drug metabolism.

Question 2. Why would I test for variations in CYP2D6 and CYP2C19 when monitoring prescription drugs?

Genetic variations in a patient’s CYP2D6 and CYP2C19 genes can help explain unusual results:

Some prescription medications are converted/metabolized to a more active form. If the patient is a poor metabolizer, he/she may not experience adequate pain relief.

If drug is detected and there is no metabolite detected, the genetic test may help determine if the patient is not taking the analgesic properly or is a poor metabolizer.

If neither drug nor metabolite is detected, or if only the metabolite is detected, this test may help determine if the patient is not taking the analgesic properly or is an ultra-extensive metabolizer.

If the patient is a nursing mother and an ultra-extensive metabolizer, codeine therapy should be carefully controlled to prevent neonatal morphine toxicity.

Question 3. What else affects the metabolism of analgesics?

Other drugs and some foods can affect analgesic metabolism. If a drug or food stops the CYP2D6 enzyme from metabolizing the analgesic normally, the patient may not experience expected outcomes for pain relief.

Question 4. What about other CYP enzymes? Are there tests for them?

Drugs are often metabolized by more than 1 enzyme. Other tests we provide for enzymes related to analgesic metabolism are individual tests for genetic variants in CYP3A4 (Test Code 91617) and CYP3A5 (Test Code 91618), and the combined CYP3A4/ CYP3A5 (Test Code 91597) genotype test. We are in the process of developing tests and interpretations for other genes.

Question 5. How do I know which enzymes/genes metabolize the drug in which I am interested?

There are many excellent resources available on the internet (such as www.drugs.com, professional version). We are also developing resources to help physicians understand the enzymes/genes of interest.

This FAQ is provided for informational purposes only and is not intended as medical advice. A clinician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.